Another project leverating the raspberry pi for some interesting stuff on another Video Game machine. What's neat about this one is that because of the simple architecture of a lot of these older machines, the raspberry pi can basically take over the CPU's job and still use the rest of the hardware of the machine.
The Vectrex CPU, a Motorola 68A09 running at 1.5MHz, controls all of the I/O including display, sound, and controls, via a 6522A VIA chip. These are both connected to the cartridge port, and with the CPU disabled using the HALT signal also at the cartridge port, all of the Vectrex's functions can be controled by an external device. In this case we're using a Raspberry Pi Zero with a 1GHz ARM CPU and 512MB of RAM, powerful enough to emulate arcade machines with vector displays, emulate the Vectrex CPU to load ROM images akin to a multicart, and run custom games written to take advantage of the greater processing power.
The Vectrex is pretty rad. I did a video on mine five years ago. I still have a couple things to fix on it someday - think the video board needs a tune up so it's a little more stable.